Tanning with periodate oxypolysaccharides



United States Patent TANNING WITH PERIODATE OXYPOLY- SACCHARIDES PercyA. Wells, Abington, Edward M. Filachione, Philadelphia, and Martin L.Fein, Elkius Park, Pa., assignors to the United States of America asrepresented by the Secretary of Agriculture No Drawing. ApplicationNovember 15, 1957 Serial No. 696,884

8 'Claims. (Cl. 8-94.33) (Granted under Title 35, U.S. Code (1952), see.266) A non-exclusive, irrevocable, royalty-free license in the inventionherein described, throughout the world for all purposes of the UnitedStates Government, with the power to grant sublicenses for suchpurposes, is hereby granted to the Government of the United States ofAmerica.

This application is a continuation-in-part of the copending applicationTanning With Periodate Oxypolysaccharides, Serial No. 553,673, filedDecember 16, 1955, now abandoned.

This invention relates to the tannage of hides, skins and leather by useof periodate-oxidized polysaccharides, and particularly to tannage withthe periodate-oxidized polysaccharides such as oxystarch, oxycelluloseand oxydextrin.

By hides, skins and leather we mean to include all animal hides, skinsand furs that are commercially tanned, and in particular, cowhide,horsehide, calfskin, pigskin, sheepskin and goatskin, as well asleathers made by the conventional tannage of such hides.

Polysaccharides, as the word is used here, means polymeric materials,the repeating unit of which is the anhydroglucose unit. The number ofsuch units in a polymer is unknown but large, so that the term does notinclude such low molecular weight materials as dior trisaccharides orother so-called oligosaccharides. Typical polysaccharides includecellulose, starch, dextrins, dextrans and related materials.

Pediodate oxypolysaccharides and periodate-oxidized polysaccharides areterms applied to the oxidation products of certain processes whereby inthe aforementioned polysaccharides a carbon-to-carbon bond is cleavedand two aldehyde groups are formed from an anhydroglucose unit asillustrated by the following structures:

CHzOH CH2OH New and efficient processes for the production of thesematerials are described in US. Patents 2,648,629 and 2,713,553. Althoughthe active oxidizing agent in most processes is periodic acid, periodatesalts may also be used as the oxidizing agent. Regardless of whetherperiodic acid or a periodate salt is employed, the products of thisspecific type of oxidation of polysaccharides are usually referred to asperiodate oxypolysaccharides when considered collectively, and forpurposes of this application the particular products will be referred toas simply oxystarch, oxydextrin or oxycellulose.

The extent of oxidation, as described, of a polysaccharide such asstarch can be readily controlled, and a complete range of aldehydederivatives of starch is made available as the oxidation level variesbetween zero and 100 percent. At 100 percent oxidation eachanhydroglucose unit is converted to the dialdehyde structure; at 50percent oxidation half of the anhydroglucose units are so altered. Fullyoxidized commercial products usually analyze 95 to 100 percentdialdehyde units. Oxystarch, also known as dialdehyde starch, is thus anopen chain polymer containing aldehyde groups, and, if no other bondrupture occurs, should have the same molecular weight as the starch fromwhich it was made. Oxy- 0 dextrin and oxycellulose are the periodate(periodic acid) oxidation products of dextrin and cellulose,respectively, and a similar analogy applies to the molecular weights ofthe oxidized products in regard to that of the polysaccharide from whichthey were prepared. When the polysaccharide has been oxidized to a levelless than fully oxidized it is generally considered that theanhydroglucose units were attacked in a substantially random fashion sothat the product is a polymeric material made up of more or less randomsequence of anhydroglucose and dialdehyde units whose structures arethose shown above. a

We have discovered that periodate oxypolysaccharides may be employed astanning agents to provide smoothgrained, light-colored tanned hideswhich had good leather characteristics.

In general, according to the invention a periodate oxypolysaccharide,that is, a polysaccharide such as starch, dextrin or cellulose in whichabout 10 to preferably at least about 30%, of the anhydroglucose unitshave been converted by means of periodic acid or periodate oxidation todialdehyde units characterized by the formula is solubilized either bygently warming a suspension of the periodate oxypolysaccharide in diluteaqueous alkali until the oxypolysaccharide is solubilized, or byautoclaving an aqueous suspension of the oxypolysaccharide for about 30minutes at about C. to obtain a solubilized oxypolysaccharide, and anaqueous solution containing the solubilized periodate oxypolysaccharideand having a pH in the range of about 4.5 to 10, is applied to the hideuntil the hide is tanned. In an alternative process the periodateoxypolysaccharide is added as a solid directly to an alkaline solutionpreferably in the pH range of about 7 to 10 containing the hide to betanned, and solubilization in the aqueous alkaline solution and tanningof the hide proceed concomitantly.

Because of its abundant supply, low cost and high reactivity, starch isour preferred raw material for the preparation of our tanning agents.Oxystarch is preferably made according to the above cited patentswhereby the expensive reagent, sodium periodate, is constantlyregenerated electrolytically during the reaction, thus making oxystarch(dialdehyde starch) potentially available at low cost. As thus produced,however, oxystarch is not appreciably soluble in water at roomtemperature and must be solubilized prior to or during the tanningprocess in order to act as a tanning agent. Among the various methodsfor its solubilization, two are particularly convenient. The firstconsists of solution in hot water, preferably by autoclaving an aqueoussuspension of oxystarch at about 120 C. for about 30 minutes. The secondconsists of dissolving the oxystarch in dilute aqueous alkali such assodium hydroxide, sodium carbonate, sodium bicarbonate, magnesium oxide,and other salts or oxides which in water give a solution whose pH is atleast 7, preferably in the range of 7 to 10. In the second method,solution of the oxystarch is expedited, if such is desired, by gentlywarming the aqueous medium. Either method yields a product entirelysuitable for our purpose. The other periodatc oxypolysaccharides canbe'similarly solubilized and used in the present invention. Hides to betanned with periodate oxypolysaccharides require no special preparation,the same preliminary treat- ,ments that are used. before conventionalvegetable, ,irnineral .or syntan tannage being entirely satisfactory. Inmaking leather for certain purposes it is sometimes advantageous toutilize a combination tannage wherein a f conventional vegetable,mineral or syntan tannage is com- Y-bihed with periodateoxypolysaccharide tannage, in which case either tannage may be appliedfirst or, if desired, the {two tanning agents may be used concurrently.f: 1' 'The practice of the invention is illustrated by the fol-,lowingexamples.

EXAMPLES 1 TO 20 was divided into four parts so that the pH of thesegrams were added to "120 grams of the dialdehyde starch solution (3:1float) in bottles which were gently agitated at room temperature byrolling on a jar mill. Small portions of these specimens were removedafter 2, 6, 24, and 72 hours of treatment for determination of shrinkagetemperature and leather-like drying after washing in running water forone day. These data are presented in Table I.

V EXAMPLES 21 TO 29 One part of fully oxidized oxystarch (95 to 1007dialdehyde units per molecule) was suspended in about 1 /2 parts of 0.1N (0.4%) aqueous sodium hydroxide. The suspension was gently warmed on asteam bath, with constant stirring, until, after a few minutes, thesolid dissolved to form a fiuid yellow solution. When diluted with waterto 10% solids content this solution had a pH of about 7. Pickledcalfskin was depickled, adjusted to the isoelectric point (pH 4.8),washed, and cut into 1 x 3 inch strips. Five strips (about 6 grams dryweight) were placed in a bottle with ml. of a 5% aqueous solution ofsolubilized, fully oxidized oxystarch. Various salts'and buffers wereadded to different bottles as shown in Table II and the bottles agitatedat room temperature by rolling on a jar mill. Shrink temperatures (Ts)were determined at various time intervals to measure the extent of thetanning action. The tanned products were washed, air- Table I TANNING OFOALFSKIN WITH OXYSTARCH'MUTOCLAVEE Treatment Shrinkage Temp., 0., After-LLD Example Alter No. Dialdehyde Hrs. Content, Butler pH 7 ZHra. 6Hrs.24Hrs. 72 Hrs. Neutr.

Percent a Y 1 95 to 98' HOAc-NaOAm". 4.9-5.0 v61 72 76 78 24 i 95 to 980.3 N'NaHGO;--- 7.3-8.2 74 80 81 83 82 6 3 95 to 98 1% M20 9.6-9.5 v6179 83 79 24 4 95 to 98 MRO+NaHCO:- 9. 4-8. 9 69 85 86 87 86 6 5 71HOAc-NaOAo. 4. 9-5.0 66 70' 74 24 6.. 71 0.3 N NaHCO; 7.3-7.8 68 74 8182 80 6 7.- 71 1% MgO. 10.1-10.2 53 63 73 74 70 72 8-- 71' MgO+NaHCOi10.0-9.8 68' '80 83 79 77 6 9.. HOAo-Na0Ac. 5.0 66 68 72 24 10- 60 0.3 NNaHCO1-.-. 7. 2-7. 7 67 ,1. 72 78 81 79 o 11 60 1% Mg() 10.2 55 62 69'74 72 72 12 60 MgO+NaHGO; 9.6-9.4 73 80 83 84 79 2 1 29 HOAc-NaOAc..-5.0 61 62 64 72 1 29 0.3 N NaHO0;... 7'. 1-8.6 63 66 74 82 78 24 1 291%M 0 10.6-10.4 56 6,1 68 68 63 72 16 29 v 10. 10.3 72 73 3 77 76 73 217 10 5.0 60 60 62 72 18 10 7.4-8.8 62 61 68 77 73 19...--.. 10 10.6-10. 2 53 53 64 63 62 72 Na7S04 (added after Sample tanned forvsolutions when used for-tanning regions of approximately 5, 8, and 10by the use of acetate, bicarbonate, magnesium oxide, and mixedbicarbonate-magnesium oxide buffers, respectively. Small pieces ofdrained pickled calfskin, 4 x 6 inches, or about autoclavmg) I a bExtent 0! anhydroglucose units of starch converted to dialdehydestructure.

3 days then neutralized in acetate bufler Time 0! taming which producedspecimen showing leather-like dry were maintained in the 55 dried, andexamined for Tanning solution: 5% solution concentration with respect tooxystarch (solubilized in autoclave), 10% in (pH '01:. 1;) for 2 hours,then washed.

appearance, flexibility and leather-like properties. The leatherobtained in these examples was very light colored and, with theexception of those tanned at pH values below.about.4.5, wasfirm and fulland flexibl Table II TANNING 0F OALFSKIN WITH SOLUBILIZED PERIODATEoxYs'rARcH Ts, in 0., After-Hours Ex. No. Butler '7 Salt I pH 12ssz44s7z104.1 s1 63' 70 71 71 4.2-4.3 5s s9 s5 67 as 4.7-4.2 s7 s9 7s 7o 5.1-5.372 73 7e 77 7a '8.3-7.6' 75 77 77 77 77 7s 8.1-8.0 72 75 79 so 819.4-8.6 70 7o 74 '74 77 8.3-7.2. 64 e4 68 '69. 71 10.1-9.8 as 71- 7s 747s ',$alt,when used, was at a coneentration'ot5%.-..-

EXAMPLES 30 TO 44 For each example a solution of sodium sulfate in waterwas prepared and sufiicient sodium bicarbonate or magnesium oxide (ormixtures of these two alkaline agents) added to make the solutions 0.3 Nin NaHCO and/or 1% in MgO. To 120 grams of one of the buffered solutionswas added 6 grams of oxystarch and a 4 x 6 inch piece of drained pickledcalfskin. The order of introducing the pickled hide and the oxystarch isimmaterial. In these examples oxystarch with levels of oxidation of 95to 98, 71, 60, 29, and 10%, respectively, were employed with each of thethree buffer solutions. Agitation was provided by carrying out thetreatment at room temperature while the bottles were rolled on a jarmill. The oxystarch gradually dissolved during the earlier stages of thetreatment. The results are presented in Table III.

Comparison of the data of these examples with that of the examples ofTable I reveals that'tanning with the solid oxystarch at pH 7 to 8 wasslower than with oxystarch solubilized by autoclaving, probably becausethe solid material dissolved rather slowly at this pH. In drum tannageof hides this is advantageous since it provides an automatic means forthe gradual increase of aldehyde concentration in the tanning solutionand facilitates the production of a smooth-grained leather.

In general, comparable results were obtained with comparable systemsregardless of the method of solubilizing the oxystarch. The tanningaction of oxystarch of 10% dialdehyde content was very slow, and, undercertain conditions resulted in poorly tanned leather. Examples 2, 6, 10and 14 (Table 1) illustrate the attaining of approximately the sameshrinkage temperature (Ts about 80 C.) with oxystarches ranging from 98down to 29% in dialdehyde content, although the rate of tanningdecreased with decreasing dialdehyde content. In practical operation ofthis invention we prefer to use oxystarch of at least about 30%dialdehyde content.

Although presence of bu'lfers and certain salts during tanning withperiodate oxypolysaccharides influences the rate of tanning and thequality of the leather products, Examples 23 and 24 (Table II)illustrate that hides are tanned in the absence of both buffer and salt(pH about naturally required a somewhat longer time for completepenetration and tanning action but the final result was equallysatisfactory. While in the examples cited we employed tanning solutionscontaining 5% by weight of oxystarch, other levels of concentration ofoxystarch have been used with satisfactory results. For example,sheepskins were tanned with an aqueous solution containing about 2.5%oxystarchto give a leather of good quality.

When other solubilized periodate-oxidized polysaccharides such asoxycellulose and oxydextrin are used instead of the oxystarch of theabove examples, substantially equivalent results are obtained.

The tanning agents 'of this invention have been described in terms ofthe present practical method, namely periodate oxidation, of makingthese particular oxidation products, that is, those in whichanhydroglucose units are converted to dialdehyde units. Since it is thechemical properties of these oxidation products that are critical to theinvention, the same type of oxidation products obtained by a differentprocess would be equally applicable to the present invention.

An interesting feature of the data in Tables I and III is the comparisonof the magnesium oxide system with a mixture of this oxide and sodiumbicarbonate to control the pH. Even though the pH of these two systemswas substantially the same, the latter system resulted in a much morerapid tanning action and was preferable to the former.

We claim:

1. A process of tanning a hide comprising applying an aqueous solutionof a periodate oxypolysaccharide containing at least about 30%dialdehyde units of the formula and selected from the group consistingof oxystarch, oxycellulose, and oxydextrin at a pH in the range of aboutfrom 4.5 to 10 to the hide until the hide is tanned.

2. The process of claim 1 wherein the periodate oxypolysaccharide isoxystarch.

3. A process of tanning a hide comprising solubilizing Table III TANNINGOF CALFSKIN WITH OXYSIARCH (DRY) Treatment Shrinka e Tem 0., Afterg pLLD Example After No. Dialdehyde Hrs. Content, Bufier pH 2 Hrs. 6 Hrs.24 Hrs. 72 Hrs. Neutr.

Percent 30 98 0.3 N NaHCO3-- 7. 5-8. 2 64 73 81 83 83 24 98 MgO, 1% 9.5-9. 4 53 66 81 84 80 24 98 MgO+NaHC O3.-- 9. 5-8.8 80 83 86 87 85 2 71NaHC Oa 7. 4-7. 8 63 70 80 82 80 24 71 MgO 10.3-10. 2 59 63 71 75 74 7271 MgO+NaHC O3"- 10. 8-8. 8 74 77 82 83 79 2 60 NaHCOa 7.3-8.0 62 78 8184 83 6 60 MgO 9. 5-9. 6 57 60 73 77 74 24 60 MgO+N2HC O 9. 3-9. 0 76 7887 85 86 2 29 NaHO O3 7. 4-8. 6 67 71 79 85 83 24 29 MgO 9. 6-9. 8 63 6366 69 70 72 29 MgO+NaHC Os..- 9. 4 74 82 86 83 79 6 NaHC O3 7. 3-8. 9 6466 74 80 78 24 10 MgO 9.7-9.9 55 62 66 64 72 10 MgO+NaHC O3. 10. 3-9. 866 72 70 67 6 Tanning solution: 5% on solution basis with respect tooxystarch (added dry), 10% in NMSOL.

b See footnote Table I. v See footnote Table I. 9 See footnote Table I.

4.5), or in the presence of sodium chloride only (pH about 5),respectively.

When split cowhide was substituted for calfskin in the above examplessubstantially the same tanning action was observed. Full thicknesscowhide and similar heavy hides a periodate oxypolysaccharide containingat least about 30% dialdehyde units of the formula O-GH-CHOCH- (IJHO([JHQOH JHO I and selected fromthe group consisting of oxystareh,oxyfhllulose; andgoxydextrin by gently warminga suspension of theperiodate oxypolysaccharide in dilute aqueous alkaliuntil the"oxypolysaccharide is dissolved, and then applying an aqueous solution ofthe solubilized oxypoly- :fsaccharideat a pH in the range of about from4.5 to 10 to the hide until the hide is tanned.

L 4. The process of claim 3 wherein the periodate oxypolysaccharideisoxystarch.

'5. A process of tanning a hide comprising solubilizing "a periodateoxypolysaceharide containing at least about minutes at about 120 C.,and'then applying an aqueous solution of the solubilizedoxypolysaccharide at a pH in the range of about from 4.5 to 10 to thehide until the hide is tanned. t

6. The process of elaim 5 wherein the periodate oxypolysaccharide 'i'soxystarch.

-: 1 7. A process of tanning a hide comprising "adding the hide anda'solid periodate oxypolysaccharide containing at-least about 30%dialdehyde units of the formula (0(|3H(|3H0CH- CHO CHnOH HO and selectedfrom the group consisting of oxystarch, oxycellulose, and oxydextrin toan aqueous solution at-apH inthe range of about from 7 to 10, andagitating the resulting mixture until the hide is tanned.

8. The process of claim 7 wherein the periodate oxypolysaccharide isoxystarch.

References Cited in the file of this patent UNITED STATES PATENTSSchmidt May 26, 1925 OTHER REFERENCES Kerr: Chemistry and Industry ofStarch, 2nded.,

-Academic Press, N.Y.C., 1950, pp. 328-329.

1. A PROCESS OF TANNING A HIDE COMPRISING APPLYING AN AQUEOUS SOLUTIONOF A PERIODATE OXYPOLYSACCHARIDE CONTAINING AT LEAST ABOUT 30%DIALDEHYDE UNITS OF THE FORMULA